This invention relates generally to a scintillation camera utilized for nuclear medical diagnosis and, in particular, to a radiation distribution imaging apparatus for use in such a camera.
The scintillation camera is an apparatus with which, after radioactive material marked with a radioisotope is administered in the body of a patient, distribution of the radioactive material in the body is measured from the outside of the body to make an image for diagnosis. U.S. Pat. No. 3,717,763, of common assignee herewith, discloses such a camera.
In case of examination with the scintillation camera, the degree of accumulation of the radioactive material in specified organs, tissue or tumors of the patient contrasts with other portions of the body. In case the localized density ratio of radioisotope distribution in the patient is relatively large, the density ratio of scintigrams, which are sequentially made, become large in proportion to the distributions in other parts of the body, so that the analysis of the scintigrams can be easily performed. However, in some cases the localized density ratio of the radioisotope distribution in the patient is relatively small. For example, in the case that an examination for tumors is being performed, taking a characteristic of tumor affinity for gallium 67 (67GA), an accumulation ratio of the tumor portion to the normal portions of the body is about 10:9 7. Such a ratio is substantially the same as the normal density contrast ratio of the scintigram itself as provided by the scintillation camera. In fact, it must also be considered that the accumulation ratio, as shown, is a little lower than the actual accumulation ratio because of the influence of blur due to the resolution of the scintillation camera. In such a case, it is very difficult to identify tumors with reference to the obtained scintigram. So, it is strongly desired to obtain scintigrams which reflect identifiable density differences, i.e., that the actual differences be reflected and emphasized.
It has been long known to utilize a scintillation scanner in a nuclear image examination wherein a detector is adapted to scan one by one at measuring points of the patient's body. Therefore, it can easily perform, to a dot only, at the scanning points, which count value is over a predetermined discriminating count level. The density ratio of the radioisotope distribution can thereby be emphasized.
But in recent years the scintillation camera has been increasingly utilized because the scintillation scanner needs a long time for scanning and the resolution and the efficiency of the scintillation camera have overtaken and outrun those of the scintillation scanner. However, in scintillation cameras of the prior art, only one detector catches all of the effective visual field, and only from this one detector is the radioisotope distribution in the field displayed in its entirety. It has been known in the past to show only the parts of the display which exceed a predetermined discriminating level of the scintigram image data as obtained by the scintillation camera with a data processor utilizing a computer. However, the latter technique has shortcomings in that an expensive data processor is needed and the original resolution of the camera is impaired by a rough digitalizing of the obtained image data.
It is known, as taught in U.S. Pat. No. 3,717,763, referred to above, to analyze the pulse heights of radiation registered by the scintillation camera and to screen out radiation points which are no more intense than the background electronic noise. This is achieved by controlling access to each point of the display and issuing an unblanking signal by the pulse height analyzer as to that point when the signal from the camera head as to that point is acceptable.